This disclosure is based upon, and claims priority from French Application No. 99/00196, filed on Jan. 11, 1999 and International Application No. PCT/FR99/03282, filed Dec. 23, 1999, which was published on Jul. 20, 2000 in a language other than English, the contents of which are incorporated herein by reference.
The invention relates to the field of integrated circuit chips.
The present invention relates to more particularly a method for protecting an integrated circuit chip in order to insulate its flanks when the chip is connected with a connection terminal block.
The connection of integrated circuit chips with a connection terminal block on a card, for example, can be effected by traditional wiring or by other techniques using conductive polymer compounds in contact with the output pads on the chip.
The traditional technology of wiring for the connection of chips requires no specific characteristic for the component constituting the integrated circuit. However, such a technology is tricky and expensive. This is because wires, generally made from copper, nickel or gold, connect the output pads on the chip to the connecting tracks of the printed circuit by soldering. In addition, this wiring technique requires high-precision equipment for making the connections, which causes a slow-down in the manufacturing rate.
In order to mitigate the drawbacks of this traditional technology, use is being made more and more often of conductive polymer compounds establishing contact between the output pads of the chip and the connecting tracks of the connection terminal block.
A first method using a conductive polymer compound for connecting the chip to the connecting tracks is illustrated in FIG. 1.
In such a case, the connecting tracks 12 are brought close to the location provided for the chip 100. The latter is bonded by the rear face 104 to the connecting tracks 12 of the connection terminal block using an insulating glue 15. This glue can for example be an adhesive cross-linking under the effect of exposure to ultraviolet radiation.
The electrical connections between the output pads 120 on the chip 100 and the connecting tracks 12 are then made by dispensing a conductive resin 40 which covers the output pads 120 on the chip 100 and the connecting tracks 12 on the card. This conductive resin 40 can for example be a polymerisable glue containing conductive particles such as silver particles.
A second method using a conductive polymer compound for connecting the chip to the connecting tracks is illustrated in FIG. 2. This method consists in attaching the chip according to a well-known mounting of the xe2x80x9cflip chipxe2x80x9d type.
In a mounting of the xe2x80x9cflip chipxe2x80x9d type, the chip 100 is turned with the active face with the output pads 120 downwards. The chip 100 is then connected by placing the output pads 120 on the connecting tracks 12 printed at the location provided for the chip.
In the example illustrated, the chip 100 is connected to the connecting tracks 12 by means of a glue 35 with isotropic electrical conduction, well-known and often used for the surface mounting of passive components.
These techniques of connecting chips by means of conductive polymers are very effective and of high performance. They have many advantages compared with the traditional technique of wiring and is tending to become widespread amongst integrated circuit assemblers. This is because these techniques use a conductive polymer making it possible to reduce the number of manufacturing operations so as to appreciably reduce the manufacturing cost of the materials of the integrated circuits.
Nevertheless, the inventors have detected a particular problem which is directly related to these connection techniques when the substrate used has a conductive flank.
It can be seen clearly in FIG. 1 that the conductive resin 40 covers the flanks 106 of the chip 100. It has however been established that, in certain cases, a conductivity on the flank 106 of the chip 100 can give rise to electrical malfunctioning of the integrated circuit. This is because, depending on the type of substrate used, the flank of the chip is insulating or conductive. If the flank is insulating, there is no problem with the conductive resin 40 being in contact with the edge.
Nevertheless, in the case where the substrate used for manufacturing the integrated circuit chip has a conductive flank, this technique cannot be used.
Likewise, it can be seen clearly in FIG. 2 that the conductive glue 35 can be caused to rise slightly on the edges of the chip 100 and thus cause electrical malfunctioning of the integrated circuit.
The solution used up to the present time consisted quite simply in not using this type of connection technique with chips having conductive flanks. This solution is however not satisfactory since it greatly limits the possibilities of the assembler, obliging him to use certain products with certain assembly techniques.
In fact the conductivity of silicon is directly related to the wafer manufacturing process and differs according to the manufacturers and the production lines. A user wishing to specify a particular conductivity of the substrate will then be linked to a given supplier and even to a given product range, which automatically gives rise to additional cost and a limitation in the products which he may use.
The purpose of the present invention is to resolve the problems disclosed above.
The purpose of the present invention is to eliminate the drawbacks related to the connection of the integrated circuit chips by technologies using conductive polymers.
To this end, the present invention proposes a method for protecting the flanks of integrated circuit chips in order to insulate them from the conductive polymer components used for. connecting the output pads of the chips with the connecting tracks of the connection terminal blocks.
In particular, the present invention proposes a method for protecting integrated circuit chips on a silicon wafer, the wafer having a front face on which the integrated circuit chips are disposed and an opposite rear face, characterised in that the method comprises the following steps:
cutting out the silicon wafer so as to disconnect the integrated circuit chips;
applying a fluid insulating material to the rear face of the wafer so as to cover the flanks of each integrated circuit chip with a thin insulating layer.
The method for protecting integrated circuit chips according to the present invention is also characterised in that it additionally comprises a step of transferring the cut-out wafer, with the rear face upwards, onto a support so as to ensure the cohesion of the chips during the application of the insulating material.
According to one characteristic, the application of the insulating material is effected by spraying on the rear face of the chips.
According to another characteristic, the application of the insulating material is effected by screen printing using a doctor blade and a screen on the rear face of the chips.
According to another characteristic, the application of the insulating material is effected by pouring on the rear face of the chips.
According to another characteristic, the application of the insulating material is effected by dipping the chips in a tank containing the insulating material.
According to another characteristic, the application of the insulating material is effected by dispensing the insulating material on the rear face of the chips, the said chips being placed on a rotating rotary tray.
According to one characteristic, the insulating material has low viscosity so as to run along the flanks of the chips.
According to another characteristic, the insulating material consists of a resin of the epoxy type having high hardness and good adhesion to the silicon.
According to another characteristic, the insulating material consists of an insulating lacquer with a low dry extract so as to obtain a thin insulating coating.
According to another characteristic, the insulating material consists of a coloured resin so as to allow a check on the areas covered with the insulating material.
According to another characteristic, the check on the areas covered with the insulating material is effected by computer-aided vision (CAV).
The method for protecting integrated circuit chips according to the present invention is also characterised in that it comprises the following steps:
deposition of a protection on the rear face of the silicon wafer;
cutting out the silicon wafer so as to disconnect each integrated circuit chip;
transferring the disconnected integrated circuit chips, rear face upwards, onto a support;
removing the protection from the rear face;
applying an insulating material to the rear face and the flanks of the chips;
ejecting the chips from the support;
connecting the chips.
According to one characteristic, the protection of the rear face of the silicon wafer consists of an adhesive which is degradable under ultraviolet, the said adhesive being degraded after the step of cutting out the wafer and removed by peeling off.
According to another characteristic, the support is a degradable adhesive exposed to ultraviolet radiation after application of the insulating material.
According to another characteristic, the ejection of the chips is effected by breaking the insulating material deposited on the support between the chips.
According to another characteristic, the ejection of the chips is effected by cutting the support.
According to another characteristic, the insulating material consists of a photosensitive resin polymerised through a mask at the level of the rear faces and flanks of the chips.
According to this characteristic, the chips are disconnected by exposing the wafer to ultraviolet radiation through a mask so as to facilitate the ejection of the chips.
The present invention also relates to an integrated circuit chip characterised in that it comprises an insulating material applied to its flanks so as to constitute a protection.
According to another characteristic, the insulating material covering the flanks of the chip consists of a resin of the epoxy type and/or an insulating lacquer and/or a polymerised photosensitive resin and/or a coloured resin.
The method according to the invention has the advantage of allowing the systematic use of techniques of direct connection between the output pads of a chip and the connecting tracks of a terminal block with a conductive glue whatever the chip used.
The method according to the invention can advantageously be used with any type of chip whatever the substrate used, whatever the size and shape of the chip, and whether or not it has protrusions.
The method according to the present invention is easy to implement. Although it requires an additional step preceding the connection of the chips, the protection method according to the invention does not give rise to any significant additional cost nor extended manufacturing time.